RC was right.
But, the problem didn't lie with the rifle. It's your loading technique that is causing the problem.
I see the same thing with many .30/30's.
You are over sizing the fired cases. YOU are inducing the excessive headspace by pushing the neck back when you size the cases. When you do fire a factory equivalent load, you are stretching the case when it is forced back against the bolt face. Fortunately, you've been loading very light and the primer is backing out, but the chamber pressure isn't heavy enough to stretch the case back which also reseats the primer....
If you keep it up, you are GUARENTEED to have more case head seperations. I'd suggest the following process, or buy/make your own broken shell extractor.....
I'm a great fan of the .22Hornet.... And it will do the same thing if cases are over-sized. The only "broken case" seperation I've ever had was with the Hornet. But, then again, it was some 40yr old brass that had the incipient case head "bright ring", and I had relegated it to "mouse fart" cast bullet loads with 1.8gr of Bullseye for .22lr sub-sonic duplication loads.
But, I get better accuracy if I reduce the case head area to remove the out-of-roundness of my fired brass due to a sloppy cut chamber (Ruger... go figure!! Third one I've had with same problem....).
Size cases just to "touch" the shoulder of the case with the die.... This is called "partial full-length sizing"...
I too have gotten excellent accuracy from the 35gr Hornady's as well as some 33gr "Blem" Remington Accu-tips (Green tip V-max's for .22wrm....). I load them over a similar charge of #2400 for around 3,000fps. Pressure is low even in the Hornet....
You really must try Hod. Lil'Gun. It's amazing in the Hornet and Bee !!!